Table of Contents
- 1 What are the factors that affect critical micelle concentration?
- 2 How CMC is affected by the presence of hydrophobic and hydrophilic groups?
- 3 Why does CMC decrease with increasing chain length?
- 4 Why does CMC decreases with increasing chain length?
- 5 What happens above critical micelle concentration?
- 6 Why does surface tension increase after CMC?
- 7 What is the critical micelle concentration (CMC)?
- 8 How does micelle formation compensate for loss of entropy in polar solvents?
What are the factors that affect critical micelle concentration?
There are several factors affecting the CMC point of a surfactant. These include the amphiphile chain length, dissolved salts, the structure of the head group, temperature, the structure of the alkyl chain and polar additives.
How would the CMC change if you increased the alkyl chain length of the surfactant?
The cmc values decrease gradually as the alkyl chain length increases.
How CMC is affected by the presence of hydrophobic and hydrophilic groups?
You are correct that generally speaking a larger hydrophobic group and the same hydrophilic headgroup should give surfactants with lower CMC. CMC is determined by the solubility of the individual surfactant molecules or ions. Therefore a larger hydrophobic group generally lowers the solubility and thus CMC.
What changes drastically at critical micelle concentration?
Below the CMC micelles are not present and the surface tension of the solution decreases and osmotic pressure increases with an increase in surfactant. Above the CMC, the concentration of unaggregated surfactant will stay constant and the number of micelles will increase as the total surfactant concentration increases.
Why does CMC decrease with increasing chain length?
Increasing the chain length decreases the CMC by increasing the hydrophobic nature of the surfactant. Adding a salt decreases the CMC by decreasing repulsions between the charged heads of the surfactant molecules. The concentration at which micelles start to form is called the Critical Micelle Concentration (CMC).
Why is critical micelle concentration important?
Significance. A knowledge of the CMC is very important when using surfactants. When the formation of micelles is desirable, e.g. when cleaning, the CMC is a measure of the efficiency of a surfactant. Variables for the scientific characterisation of the surface adsorption can also be derived from the CMC.
Why does CMC decreases with increasing chain length?
How does chain length affect critical micelle concentration?
A physical chemistry experiment is presented that examines the effect of hydrocarbon chain length on the critical micelle concentration of three alkyltrimethylammonium bromide compounds. The results verify that the CMC decreases with increasing hydrocarbon chain length.
What happens above critical micelle concentration?
The CMC is an important characteristic of a surfactant. Before reaching the CMC, the surface tension changes strongly with the concentration of the surfactant. After reaching the CMC, the surface tension remains relatively constant or changes with a lower slope. Micelles only form above critical micelle temperature.
What happens below critical micelle concentration?
Definition. The Critical Micelle Concentration (CMC) is the concentration of surfactants in a solution above which micelles form. Below the CMC, surfactants adsorb to a surface, lowering the surface tension, or disperse within the bulk. Below the CMC, almost no micelles form, while above it, lots of micelles form.
Why does surface tension increase after CMC?
after CMC there is no further power of surfactants to reduce the tension; Associate ions, however, increase with adding more surfactant. Therefore, there is a slight increase in CMC right after micelles start to form due to micellar solubilization of the contaminant.
What happens above the critical micelle concentration?
What is the critical micelle concentration (CMC)?
The critical micelle concentration CMC is the surfactant concentration at and above which micelles are formed. It can be determined for surfactant solutions by measuring the surface tension at different concentrations.
Does hydrocarbon chain length affect the CMC of a micelle?
The results verify that the CMC decreases with increasing hydrocarbon chain length. The use of these methods to determine the fractional ionization of the micelle will also be discussed.
How does micelle formation compensate for loss of entropy in polar solvents?
The minimization of the unfavourable contact between non-polar surfactant chains and the polar solvent compensates the loss of entropy by micelle formation. In addition to the micelles shown in figure 3 so-called inverse micelles exist which cluster their head groups and orient their chains towards a surrounding non-polar phase.
What determines the concentration at which micellization takes place?
This fact depends not only on their concentration but also on their composition. The main parameter responsible for that is the hydrophobic portion of the substance, its length, as well as the polar head nature [7,11,12]. CMC represents the concentration at which the micellization starts.